Complex electronic circuits are frequently implemented by assembling a plurality of individually cased circuit modules in a supporting rack, with electrical interconnection between the modules being effected by cabling.
The electronic components within each module require cooling, and to provide such an airflow cooling fans are often installed on the front and/or back faces of each module so that air is drawn into the module through openings in the front face and is expelled through openings in the rear face.
When the modules are assembled into a rack, only the front and rear faces are accessible. As the circuit modules become more complex, the rear face of the module is increasingly taken up by the provision of connectors for linking the modules together, and the front face is increasingly occupied by devices such as indicator lights, disc drives, setting switches, etc. This increasing number and complexity of components mounted on the front and rear faces of the module leaves little room for ventilation fans or ventilation openings.